How critical is lifter/push rod preload?
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How critical is lifter/push rod preload?
I just put in a new cam, new followers, newly rebuilt heads, new carb and a few new peripherals on my 390. (The bottom end has less than 10Km and looks fine). When I first started it I had no compression in #2. I immediately ordered the next shortest push rods and replaced the entire bank (all 8), these are the shortest of the easy to find push rods. The car started and ran perfectly right away, 150 lbs. in #2. I proceeded with cam break-in. So it's running really well but I have not gone back to compress each hydraulic lifter to check preload. How critical is this? My experience is if a pushrod is too long it will simply bend. Is it possible they can be slightly long and put undue stress on the cam and potentially cause premature wear??
I appreciate the feedback.
I appreciate the feedback.
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Joined: Jun 2003
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From: Black Hills of SD
If it is slightly too long it could keep the valve from seating but probably not bend. Some engine builders and manuals say the lifter plunger should be about centered in the bore, others claim a .010 preload is fine. I usually go for the ,010. It's a lot easier to check before the lifters are pumped up.
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lifter preload and...
Hi Billy,
Thanks for the help. A couple questions. What is the best way to drain the lifter? I do not have a tool for it and I don't have the "feel." Also, I'm not sure what you mean by "lifter plunger should be about centered in the bore." Does that mean the the preload or theoretical slack (assuming the lifter were to drain while running) would prevent proper geometry of the rocker/pushrod/lifter? Finally, since the valves are fully closing and the pushrods are not bending would that indicate I am within the acceptable range or do you still suggest measuring. Ultimately my concern is risk to the new cam.
Sorry for all the questions.
Thanks, and if I could figure out how to post a pic I'd show you the cam and lifters I pulled out. Some cam lobes were little more than round, one lifter had a hole in the bottom. A mess.
Thanks again, D
Thanks for the help. A couple questions. What is the best way to drain the lifter? I do not have a tool for it and I don't have the "feel." Also, I'm not sure what you mean by "lifter plunger should be about centered in the bore." Does that mean the the preload or theoretical slack (assuming the lifter were to drain while running) would prevent proper geometry of the rocker/pushrod/lifter? Finally, since the valves are fully closing and the pushrods are not bending would that indicate I am within the acceptable range or do you still suggest measuring. Ultimately my concern is risk to the new cam.
Sorry for all the questions.
Thanks, and if I could figure out how to post a pic I'd show you the cam and lifters I pulled out. Some cam lobes were little more than round, one lifter had a hole in the bottom. A mess.
Thanks again, D
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